In today's Android-enabled world, QR codes play quite an important role because, face it, who wants to type that long, pesky URL on your phone's keyboard when you can just quickly scan an image and have the URL decoded in a split second?
Why do I say with such confidence that QR codes are now a commodity? Have a look at this awesome chart AppBrain posted yesterday. See Barcode Scanner, whose primary purpose is to scan QR codes? A whopping 63.8% of Android users have it installed on their phones - in fact it's the #3 most installed application.
Every respectable Android site uses QR codes in one way or another - sites like AppBrain offer a QR code on every application page, and when we do app roundups, like this 8 Great Apps Every Rooted Android User Should Know About one, we try to include QR images as well.